This invention relates to fire door operators, and more particularly, to a fire door operator having an integrated electronically descent control device.
Commercial doors come in a variety of configurations: rolling steel (jackshaft driven), overhead sectional (trolley driven), store front grilles (jackshaft driven), fire doors (jackshaft driven) and so on. A fire door is a specially designed commercial door which is placed in strategic locations throughout such places as factories, hospitals and schools to prevent the spread of fire through a building. In the event of a fire, the fire door closes automatically, sealing off protected areas and preventing further spread of the fire.
The most basic version of a fire door system is a fire door coupled to a door sprocket. The sprocket includes a sprocket assembly having a fusible link that normally engages a sprocket to hold the door open. In the event of a fire, when the sprocket assembly reaches a critical temperature, the link softens or melts and releases the sprocket. The door springs to close and begins to descend in the downward direction. U.S. Pat. No. 4,147,197 to Bailey et al. describes a fire door with only a fusible link for enabling closure.
A controlled descent mechanism usually prevents the door from rapidly running uncontrolled into the floor due to acceleration from gravity. Frequently, the controlled descent mechanism is a mechanical assembly, such as a viscous clutch or governor, that prevents the door from exceeding a maximum or runaway speed. An example of a fire door system having an integrated viscous clutch assembly can be found in U.S. Pat. No. 5,203,392 to Shea. Shea discloses a mechanism for controlling the raising and lowering of a fire door in which a pneumatically or hydraulically operated governor is mounted on an input shaft for limiting its rotational speed before it drives the speed reduction gearing driving the output shaft.
In addition to being operated as a fire door, some fire doors need to be operated as regular commercial doors, requiring opening and closing through a more conventional door opener system. Commercial door openers typically include a motor, a gear reduction system and an electronic control package for automatically opening and closing the door. The single operation system of many fire doors, in which the fusible link must be replaced after closing, is not suitable for such dual use.
More importantly, fire doors must be tied into the building smoke and fire alarm systems. In the event of a fire, smoke alarms can provide an earlier indication that the fire door should be closed than a purely mechanical system. In a purely mechanical system, the ambient temperature must reach a very high level to melt the fusible link before the door descends. In a fire door system connected to a smoke or fire alarm system, the fire door can be programmed to descend upon receipt of a fire alarm signal, before melting of the fusible link.
Many fire door openers are powered by AC motors. AC motors are generally lower in cost because of their higher use than DC motors. Additionally, use of an AC motor means the opener can be driven by the line voltage without any expensive DC rectification or conditioning circuitry. The major disadvantage of an AC motor, however, is they it cannot drive the system in the event of a power outage. Also, the AC brake solenoid in the reverse brake system, releases in a power outage, causing the door to drop when there is no alarm condition. Such AC motor systems are generally used in applications where the normal condition of the door is closed (normally closed or NC).
In situations where the fire door is normally opened, or remains open for significant periods of time, some fire door operators are powered by a DC motor with battery backup. If the door needs to be opened or closed during the AC power outage, the operator can be operated with the battery backup. However, DC motor systems are more expensive than AC motor systems and, in the event of a failure of the battery backup system, the unit still requires a controlled descent device, if it has a fail safe brake.
U.S. Pat. No. 5,245,879 to McKeon describes a fail-safe fire door release mechanism having automatic reset. Fail-safe operation, in the industry, means the fire door will close in the absence of power, which frequently precedes a fire. McKeon is also concerned with having a fire door that can be automatically reset in the event of a power outage. McKeon's fail-safe mechanism includes a solenoid for activating a brake. In the absence of power, the solenoid is open and disengages the brake; in the presence of power, the brake is closed and engages the brake. Thus, when power is lost (whether or not there is a fire alarm), the brake is released allowing the door to close. Door descent speed is controlled by the governor arrangement described in the Shea patent. While McKeon provides for fail-safe operation, the door always closes during a power outage.
There is a need for a fire door operator which can be driven by a low cost AC motor during normal door operation. There is also a need for a fire door operator which can reliably close the door during an alarm condition during a power outage. There is a need for a fire door operator which does not inadvertently release the door during a power outage unless there is a fire or an alarm condition. There is also a need for a fire door opener which controls the descent of the door electronically, without the added cost of an expensive viscous clutch. There is a further need for a fire door which is user configurable for alarm contact type, descent speed and time-to-close delay.